Method of making a refractory article

ABSTRACT

A method of making a refractory article is provided. The method includes: a) mixing a binder system, a refractory charge, and a second colloidal binder to form an aqueous slurry; b) casting the aqueous slurry into a mold; c) subjecting the mold containing the aqueous slurry to a temperature that is lower than a slurry casting temperature for a time sufficient to form a green strength article; and d) firing the green strength article at a temperature of at least 450° C. for a time sufficient to achieve thermal homogeneity, thereby forming a refractory article. Refractory articles made in accordance with the method have a unique combination of pore structure and mechanical properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 62/886,707, filed Aug. 14, 2019, the entirecontent of which is incorporated by reference herein.

FIELD

The present disclosure relates to a method of making a refractoryarticle. More particularly, the present disclosure relates to a methodof making a refractory article that includes forming a green strengtharticle from an aqueous slurry. The resulting refractory articles madein accordance with the method of the present disclosure have a uniquecombination of pore structure and mechanical properties.

BACKGROUND

Articles intended to be placed in harsh environments, such as elevatedtemperatures, erosive or corrosive environments, are often made ofrefractory material. Such refractory articles may be used for protectionagainst gas, liquid, or solid at high temperatures in various processesin order to perform sensing, melting, transporting, casting, etc.Refractory articles are indispensable to the metal, glass,petrochemical, and cement industries to name just a few. Refractoryarticles can be produced with a relatively low porosity (e.g., <35%) ora relatively high porosity (e.g., ±35%), which is typically reported asapparent porosity. Apparent porosity refers to the pores connected tothe surface of the refractory article (or open pores).

In refractory design, there generally exists a tradeoff between strengthand porosity. Generally, refractory articles with a high amount ofporosity have excellent insulating properties (due to the high volume ofair enclosed therein) and low bulk density, but also exhibit lesscorrosion resistance and less strength than lower porosity articles.Porosity may be desirable for any number of reasons, such as reducingthe weight of an article, improving buoyancy, minimizing energy lossthroughout the system, allowing fluid or gas flow pathways, as well asslowing crack propagation, thereby increasing the time to failure of anarticle.

However, the benefits of porosity largely assume some level of controlon the pore structure, namely the size, shape, and distribution of poresin the article. Conventional low-cost sintering techniques often lackthe ability to control porosity at a precise level and suffer fromvariations in material properties across similarly manufactured articlesor even within the same article. One of the major challenges incontrolling pore structure in the fired article is achieving uniformextraction of water from the liquid body. A non-uniform extraction ofwater results in variable shrinkage throughout the article which canlead to several undesirable outcomes such as formation of largeconcentrated pores or voids, geometrical warpage, and internal stressingor cracking of the article. There are many methods employed by thoseskilled in the art to minimize shrinkage variation, but most requiretightly controlled processing parameters (e.g., specific mixers,precision molds, controlled environmental chambers, etc.), long drytimes, or setting limitations on the design of the article or slurrycomposition to achieve higher manufacturing stability.

One interesting method for controlling water removal during forming isthrough use of aqueous freeze casting. This method involves templatingthe structure of ice crystal formation as water freezes to yield porousceramics with a specific porosity. While the method shows promise, italso has several limitations. One primary limitation is that articlesformed using this method generally have a lamellar porosity, where themajor axis of the pore is significantly longer than the minor axis ofthe pore. In theory, this lamellar structure can provide an improvedtrade-off between strength and density, if strength is only required inone direction. However, in practice with complicated shapes as well asdemands of throughput in a manufacturing setting, it is difficult toachieve the alignment of pores with the uniaxial load direction. Thispresents problems again in both manufacturing (cracking duringformation) and use. Refractory articles that have a lamellar porestructure are brittle and prone to cracking if not loaded precisely asintended. Moreover, most real-world applications are loaded in multipledirections.

Accordingly, there remains a need in the art for methods of makingrefractory articles that address the foregoing problems.

SUMMARY

The present disclosure is related to a method of making a refractoryarticle. To illustrate various aspects of the inventive concepts,several exemplary embodiments of the method are disclosed.

In accordance with the present disclosure, a method of making arefractory article is provided. The method includes: a) mixing a bindersystem, a refractory charge, and a second colloidal binder to form anaqueous slurry; b) casting the aqueous slurry into a mold, wherein theaqueous slurry is at a slurry casting temperature; c) subjecting themold containing the aqueous slurry to a temperature that is less thanthe slurry casting temperature for a time sufficient to form a greenstrength article; and d) firing the green strength article at atemperature of at least 450° C. for a time sufficient to achieve thermalhomogeneity, thereby forming a refractory article.

Other aspects, advantages, and features of the inventive concepts willbecome apparent to those skilled in the art from the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an optical digital microscope image, at approximately 100×magnification, of a refractory article made in accordance with anexemplary method of the present disclosure (scale bar is 1 mm); and

FIG. 2 is an optical digital microscope image, at approximately 100×magnification, of a refractory article made in accordance with aconventional freeze casting method (scale bar is 1 mm).

DETAILED DESCRIPTION

Disclosed herein are methods of making a refractory article and theresulting refractory articles. While the present disclosure describesexemplary embodiments of the methods and refractory articles in detail,the present disclosure is not intended to be limited to the disclosedembodiments. Also, certain elements of exemplary embodiments disclosedherein are not limited to any exemplary embodiments, but instead applyto all embodiments of the present disclosure.

The terminology as set forth herein is for description of theembodiments only and should not be construed as limiting the disclosureas a whole. All references to singular characteristics or limitations ofthe present disclosure shall include the corresponding pluralcharacteristic or limitation, and vice versa, unless otherwise specifiedor clearly implied to the contrary by the context in which the referenceis made. Unless otherwise specified, “a,” “an,” “the,” and “at leastone” are used interchangeably. Furthermore, as used in the descriptionand the appended claims, the singular forms “a,” “an,” and “the” areinclusive of their plural forms, unless the context clearly indicatesotherwise.

To the extent that the term “includes” or “including” is used in thedescription or the claims, it is intended to be inclusive in a mannersimilar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim. Furthermore, to the extentthat the term “or” is employed (e.g., A or B) it is intended to mean “Aor B or both.” When the applicants intend to indicate “only A or B butnot both” then the term “only A or B but not both” will be employed.Thus, use of the term “or” herein is the inclusive, and not theexclusive use. Furthermore, the phrase “at least one of A, B, and C”should be interpreted as “only A or only B or only C or any combinationsthereof.”

The methods of making a refractory article and the resulting refractoryarticles of the present disclosure can comprise, consist of, or consistessentially of the essential elements of the disclosure as describedherein, as well as any additional or optional element described hereinor which is otherwise useful in refractory applications.

All percentages, parts, and ratios as used herein are by weight of thetotal composition, unless otherwise specified. All ranges andparameters, including but not limited to percentages, parts, and ratios,disclosed herein are understood to encompass any and all sub-rangesassumed and subsumed therein, and every number between the endpoints.For example, a stated range of “1 to 10” should be considered to includeany and all sub-ranges beginning with a minimum value of 1 or more andending with a maximum value of 10 or less (e.g., 1 to 6.1, or 2.3 to9.4), and to each integer (1, 2, 3, 4, 5, 6, 7, 8, 9, and 10) containedwithin the range.

Any combination of method or process steps as used herein may beperformed in any order, unless otherwise specified or clearly implied tothe contrary by the context in which the referenced combination is made.

The term “green strength article” as used herein refers to an articlethat is formed from an aqueous slurry that has been sufficientlysolidified such that the article can be handled and/or manipulated.

The terms “isotropic distribution of pores” or “isotropic poredistribution” are used interchangeably herein to refer to pores in arefractory article that have a substantially uniform shape, size, andspacing throughout the refractory article. As used herein, the term“substantially uniform” means that a particular value is within 25% ofthe respective average value. For example, a substantially uniform poresize means that the size of an individual pore is within 25% of theaverage pore size in the refractory article.

The method of making a refractory article according to the presentdisclosure includes: a) mixing a binder system, a refractory charge, anda second colloidal binder to form an aqueous slurry; b) casting theaqueous slurry into a mold, wherein the aqueous slurry is at a slurrycasting temperature; c) subjecting the mold containing the aqueousslurry to a temperature that is less than the slurry casting temperaturefor a time sufficient to form a green strength article; and d) firingthe green strength article at a temperature of at least 450° C. for atime sufficient to achieve thermal homogeneity, thereby forming arefractory article. The methods of the present disclosure producerefractory articles having a unique combination of pore structure andmechanical properties.

As mentioned above, the benefits of porosity in a refractory articlelargely assume some level of control on the pore structure, such as poresize, pore shape, and pore distribution. When comparing two refractoryarticles having the same apparent porosity, a refractory article withsmaller, more uniformly distributed pores will generally be moreinsulating across 3-dimensions than a refractory article with lesscontrolled porosity. Furthermore, most real-world applications ofrefractory articles involve loading in multiple directions, whichrequires a greater homogeneity of strength (e.g., strength in multipledirections as opposed to a single (uniaxial) direction). The methods ofthe present disclosure provide refractory articles that possess agreater homogeneity of strength, as well as an improved strength toweight ratio (or strength to density ratio), due to a more isotropicdistribution of pores created in the refractory articles.

The methods of the present disclosure have yielded surprising results,allowing for the formation of refractory articles with variousrefractory materials that are lighter, stronger, more insulating, andmore cost efficient than previously possible. It is the combination ofproperties, the improved relationship between strength and density (orporosity) for a given refractory material that signifies a positive stepin the optimization of internal structure and enhanced capabilities tomeet an expanded range of specific design criteria.

Furthermore, the methods of the present disclosure can providesignificant process cost and time savings. For example, the methods ofthe present disclosure provide refractory articles with low dimensionalshrinkage, or net shape articles, which do not suffer the same warpagephenomenon associated with conventional methods. This corelates with areduction in internal forming stresses, which is realized as excellentthermal shock properties of the green strength article. In the examplesthat follow, each green strength article is taken directly from afreezer (e.g., at −80° C.) and placed into an oven (e.g., at 700° C.)with no intermediary step. This alone is a remarkable achievement andoffers the potential for significant time, cost, and space savings on amanufacturing floor. The net shape is additionally beneficial when tighttolerances are demanded. In addition, the net shape of the refractoryarticle also limits the amount of labor or machine time required toachieve specific geometries.

The method of the present disclosure includes the formation of anaqueous slurry by mixing together a binder system, a refractory charge,and a second colloidal binder. In embodiments of the present disclosure,the binder system comprises a caramelized carbohydrate component, anadjuvant, and a first colloidal binder. In embodiments of the presentdisclosure, the binder system is an aqueous liquid. Any of the mixingsteps described herein may be carried out using conventional mixingequipment, such as a high shear mixer.

In embodiments, the method of the present disclosure further includesforming the binder system. In embodiments of the present disclosure, thebinder system may be formed by preparing a caramelized carbohydratecomponent and mixing the caramelized carbohydrate component with anadjuvant and a first colloidal binder.

In embodiments of the present disclosure, the caramelized carbohydratecomponent is obtained by caramelization of a mixture comprising waterand a carbohydrate. In certain embodiments, the caramelization iscarried out by heating the mixture comprising water and the carbohydrateto a caramelization temperature, such as a temperature of 20° C. to 125°C., including 50° C. to 120° C., 60° C. to 120° C., 70° C. to 120° C.,80° C. to 120° C., 90° C. to 115° C., 100° C. to 110° C., and alsoincluding 100° C. to 105° C., for an effective amount of time tocaramelize the carbohydrate, such as a time period of at least 5minutes, including from 5 minutes to 30 minutes, from 5 minutes to 20minutes, and also including from 5 minutes to 10 minutes. One of skillin the art can readily determine an appropriate caramelizationtemperature and amount of time to caramelize based on thecarbohydrate(s) used. While the caramelization process remains poorlyunderstood, heating of the carbohydrate will form, inter alia, caramelproducts, such as caramelan, caramelen, and caramelin.

The caramelized carbohydrate component may be derived from thecaramelization of a variety of carbohydrates. In accordance with thepresent disclosure, the caramelized carbohydrate component is derivedfrom at least one of a monosaccharide, a disaccharide, a trisaccharide,and an oligosaccharide. Exemplary monosaccharides include, but are notlimited to, glucose, fructose, and galactose. Exemplary disaccharidesinclude, but are not limited to, sucrose, lactose, and maltose.Exemplary trisaccharides include, but are not limited to, maltotrioseand raffinose. Exemplary oligosaccharides include, but are not limitedto, maltodextrin, fructooligosaccharides, and galactooligosaccharides.In embodiments of the present disclosure, the caramelized carbohydratecomponent is derived from at least one of sucrose, glucose, fructose,galactose, maltose, and lactose. In embodiments of the presentdisclosure, the caramelized carbohydrate component is derived fromsucrose.

In other embodiments, a pre-caramelized, caramelized carbohydrate (e.g.,a commercially available caramelized carbohydrate) may be mixed withwater to form the caramelized carbohydrate component. In suchembodiments, the pre-caramelized, caramelized carbohydrate and watermixture need not be processed (e.g., heated to a caramelizationtemperature) to obtain the caramelized carbohydrate component.Furthermore, in such embodiments, the resulting caramelized carbohydratecomponent may be mixed with a first colloidal binder and an adjuvant toform the binder system.

In accordance with the present disclosure, the binder system comprisesan adjuvant. In embodiments, an adjuvant may be added to the mixture ofwater and the carbohydrate that is heated to form the caramelizedcarbohydrate component. Accordingly, in such embodiments, the adjuvantis a component of the caramelized carbohydrate component. Inembodiments, an adjuvant may be added to a caramelized carbohydratecomponent that is obtained by mixing a pre-caramelized, caramelizedcarbohydrate and water. The adjuvant may be one or more of an acid, aninorganic wetting agent, and an acid phosphate adhesive. Exemplary acidsinclude, but are not limited to, phosphoric acid, sulfuric acid, citricacid, acetic acid, boric acid, and oxalic acid. The acid may be usefulfor promoting caramelization of the carbohydrate at a lower temperaturethan would typically be required. Exemplary inorganic wetting agentsinclude, but are not limited to, aluminum ammonium sulfate, magnesiumsulfate, and aluminum sulfate. The inorganic wetting agent may act as awetting agent in aqueous medium for the caramel products to wet out therefractory charge. Exemplary acid phosphate adhesives include, but arenot limited to, a calcium phosphate, a magnesium phosphate, and analuminum phosphate, including monobasic, dibasic, and tribasic formsthereof, and various hydrates thereof.

In embodiments, the caramelized carbohydrate component includes at leastone of: an acid comprising at least one of phosphoric acid, sulfuricacid, citric acid, acetic acid, boric acid, and oxalic acid; aninorganic wetting agent comprising at least one of aluminum ammoniumsulfate, magnesium sulfate, and aluminum sulfate; and an acid phosphateadhesive comprising at least one of calcium phosphate, magnesiumphosphate, and aluminum phosphate. In certain embodiments, thecaramelized carbohydrate component includes phosphoric acid, which maybe obtained by a mixture of 75 wt % H₃PO₄ and 25 wt % water, aluminumammonium sulfate, which may include AlNH₄(SO₄)₂·12 H₂O, and calciumphosphate monobasic, which may include the anhydrous or monohydrateforms. In embodiments, the caramelized carbohydrate component comprisesone or more acids, and optionally comprises an inorganic wetting agentand/or an acid phosphate adhesive.

In embodiments, the caramelized carbohydrate component is formed bycaramelization of a mixture comprising 25 wt % to 75 wt % of acarbohydrate, 25 wt % to 70 wt % of water, 0.01 wt % to 25 wt % of acid,0 wt % to 5 wt % of inorganic wetting agent, and 0 wt % to 2 wt % ofacid phosphate adhesive.

In embodiments of the present disclosure, the caramelized carbohydratecomponent is formed by caramelization of a mixture comprising 40 wt % to60 wt % of a carbohydrate, 40 wt % to 60 wt % of water, 1 wt % to 25 wt% of acid, 0 wt % to 1 wt % of inorganic wetting agent, and 0 wt % to1.5 wt % of an acid phosphate adhesive.

In embodiments of the present disclosure, the caramelized carbohydratecomponent is formed by caramelization of a mixture comprising 40 wt % to50 wt % of a carbohydrate, 25 wt % to 40 wt % of water, 15 wt % to 25 wt% of acid, 0.25 wt % to 0.75 wt % of inorganic wetting agent, and 1 wt %to 1.5 wt % of acid phosphate adhesive.

In embodiments of the present disclosure, the caramelized carbohydratecomponent is formed by caramelization of a mixture comprising 45 wt % to55 wt % of a carbohydrate, 30 wt % to 40 wt % of water, 0.5 wt % to 1.5wt % of acid, 0.5 wt % to 0.75 wt % of inorganic wetting agent, and 1 wt% to 1.5 wt % of acid phosphate adhesive.

In embodiments of the present disclosure, the caramelized carbohydratecomponent is formed by caramelization of a mixture comprising 65 wt % to75 wt % of a carbohydrate, 25 wt % to 30 wt % of water, and 1.25 wt % to1.75 wt % of acid.

In certain of the foregoing embodiments, the carbohydrate comprisessucrose, the acid comprises phosphoric acid, which may be obtained by amixture of 75 wt % H₃PO₄ and 25 wt % water, the inorganic wetting agentcomprises aluminum ammonium sulfate, which may include AlNH₄(SO₄)₂·12H₂O, and the acid phosphate adhesive comprises calcium phosphatemonobasic, which may include the anhydrous or monohydrate forms. Incertain of the foregoing embodiments, the acid comprises phosphoric acidand boric acid.

In embodiments of the present disclosure, the adjuvant is added to thecaramelized carbohydrate component after the caramelized carbohydratecomponent is formed.

In addition to the caramelized carbohydrate component and the adjuvant,the binder system of the present disclosure also includes a firstcolloidal binder. In accordance with the present disclosure, the firstcolloidal binder comprises at least one of a colloidal silica, acolloidal alumina, a colloidal zirconia, a colloidal yttria, andorganically modified versions of the foregoing. One example of anorganically modified colloidal binder is Ludox® SK colloidal silica,which is commercially available from W. R. Grace & Co.-Conn. (Columbia,Md.). In general, the first colloidal binder is a suspension comprisingsubmicron-sized inorganic particles (e.g., SiO₂, Al₂O₃, ZrO₂) dispersedin an aqueous solution. In embodiments of the present disclosure, thefirst colloidal binder used to form the binder system comprises acolloidal silica.

One example of a first colloidal binder suitable for use in the bindersystem of the present disclosure is NALCO 1144 colloidal silica, whichis commercially available from Nalco Company (Naperville, Ill.). TheNALCO 1144 colloidal silica suspension has the following properties: 40wt % of colloidal silica as SiO₂; a pH of 9.9 at 25° C.; an averageparticle diameter of 14 nm; a specific gravity of 1.30; a viscosity of15 cP; and 0.45 wt % of Na₂O.

As previously mentioned, the binder system of the present disclosurecomprises a mixture of the caramelized carbohydrate component, theadjuvant, and the first colloidal binder. In embodiments of the presentdisclosure, the caramelized carbohydrate component, which may comprisefrom 0.01 wt % to 25 wt % adjuvant (based on the total weight of thecaramelized carbohydrate component), comprises from 5 wt % to 95 wt % ofthe binder system, and the first colloidal binder comprises from 5 wt %to 95 wt % of the binder system. In embodiments of the presentdisclosure, the caramelized carbohydrate component, which may comprisefrom 0.01 wt % to 25 wt % adjuvant (based on the total weight of thecaramelized carbohydrate component) comprises from 10 wt % to 90 wt % ofthe binder system, and the first colloidal binder comprises from 10 wt %to 90 wt % of the binder system. In embodiments of the presentdisclosure, the caramelized carbohydrate component, which may comprisefrom 0.01 wt % to 25 wt % adjuvant (based on the total weight of thecaramelized carbohydrate component), comprises from 15 wt % to 85 wt %of the binder system, and the first colloidal binder comprises from 15wt % to 85 wt % of the binder system. In embodiments of the presentdisclosure, the caramelized carbohydrate component, which may comprisefrom 0.01 wt % to 25 wt % adjuvant (based on the total weight of thecaramelized carbohydrate component), comprises from 25 wt % to 75 wt %of the binder system, and the first colloidal binder comprises from 25wt % to 75 wt % of the binder system. In embodiments of the presentdisclosure, the caramelized carbohydrate component, which may comprisefrom 0.01 wt % to 25 wt % adjuvant (based on the total weight of thecaramelized carbohydrate component), comprises from 40 wt % to 70 wt %of the binder system, and the first colloidal binder comprises from 30wt % to 60 wt % of the binder system. In embodiments of the presentdisclosure, the caramelized carbohydrate component, which may comprisefrom 0.01 wt % to 25 wt % adjuvant (based on the total weight of thecaramelized carbohydrate component), comprises from 55 wt % to 75 wt %of the binder system, and the first colloidal binder comprises from 25wt % to 45 wt % of the binder system. In embodiments of the presentdisclosure, the caramelized carbohydrate component, which may comprisefrom 0.01 wt % to 25 wt % adjuvant (based on the total weight of thecaramelized carbohydrate component), comprises from 60 wt % to 70 wt %of the binder system, and the first colloidal binder comprises from 30wt % to 40 wt % of the binder system. Any of the previously describedcaramelized carbohydrate components, adjuvants, and first colloidalbinders may be used in the foregoing embodiments of the binder system.

In embodiments of the present disclosure, the caramelized carbohydratecomponent comprises from 40 wt % to 70 wt % of the binder system and isformed by caramelization of a mixture comprising 50 wt % to 60 wt % of acarbohydrate, such as sucrose, 35 wt % to 45 wt % of water, 0.75 wt % to1.5 wt % of acid, such as phosphoric acid, 0.25 wt % to 0.75 wt % ofinorganic wetting agent, such as aluminum ammonium sulfate, and 1 wt %to 1.5 wt % of an acid phosphate adhesive, such as calcium phosphatemonobasic; and the first colloidal binder comprises from 30 wt % to 60wt % of the binder system and comprises a colloidal silica.

In embodiments of the present disclosure, the binder system comprisesfrom 5 wt % to 70 wt % caramelized carbohydrate component, from 0.25 wt% to 10 wt % adjuvant, and from 25 wt % to 90 wt % first colloidalbinder, based on the total weight of the binder system. In embodimentsof the present disclosure, the binder system comprises from 5 wt % to 45wt % caramelized carbohydrate component, from 0.25 wt % to 3 wt %adjuvant, and from 50 wt % to 90 wt % first colloidal binder, based onthe total weight of the binder system. In embodiments of the presentdisclosure, the binder system comprises from 55 wt % to 70 wt %caramelized carbohydrate component, from 2 wt % to 10 wt % adjuvant, andfrom 25 wt % to 40 wt % first colloidal binder, based on the totalweight of the binder system.

As mentioned above, the aqueous slurry of the present disclosure isformed by mixing the binder system together with a refractory charge anda second colloidal binder. In embodiments of the present disclosure, thesecond colloidal binder used to form the aqueous slurry comprises atleast one of a colloidal silica, a colloidal alumina, a colloidalzirconia, a colloidal yttria, and organically modified versions of theforegoing. In embodiments of the present disclosure, the secondcolloidal binder is the same material as the first colloidal binder usedto form the binder system. In embodiments of the present disclosure, thesecond colloidal binder is a different material from the first colloidalbinder used to form the binder system. In embodiments of the presentdisclosure, the second colloidal binder and the first colloidal binderused to form the binder system both comprise a colloidal silica.

In accordance with the present disclosure, the aqueous slurry includes arefractory charge. A variety of refractory charges may be used in themethods of the present disclosure. The refractory charge used to form arefractory article in accordance with the methods of the presentdisclosure may be selected based upon a variety of factors including,but not limited to, the particular application in which the refractoryarticle will be used, the particular type of chemical environment ormolten metal with which the refractory article will come into contact,and so forth.

The refractory charge according to the present disclosure may beprovided in different forms (e.g., fibrous, acicular, lamellar,granular) and may be of mineral or synthetic origin. In accordance withthe present disclosure, the refractory charge comprises one or more of asilicate, a metal oxide, a boride, a nitride, a carbide, a sulfide, afluoride, an aluminide, a synthetic glass, glass fibers (e.g., E-glassfibers), refractory ceramic fibers, non-refractory ceramic fibers,graphite, bone ash, aluminum titanate, and calcium aluminate. Exemplarysilicates include, but are not limited to, aluminum silicate, magnesiumsilicate, calcium silicate, sodium silicate, potassium silicate,zirconium silicate, mica, wollastonite, microlite, and talc. Exemplarymetal oxides include, but are not limited to, MgO, Al₂O₃, TiO₂, ZrO₂,Y₂O₃, MgAl₂O₄, and WO₂. Exemplary borides include, but are not limitedto, TiB₂ and ZrB₂. Exemplary nitrides include, but are not limited to,boron nitride, aluminum nitride, and silicon nitride. Exemplary carbidesinclude, but are not limited to, silicon carbide and boron carbide.Exemplary sulfides include, but are not limited to, BaSO₄. Exemplaryfluorides include, but are not limited to, CaF₂ and AlF₃. Exemplaryaluminides include, but are not limited to, MgAl and TiAl.

In embodiments, the refractory charge comprises at least one of boronnitride, aluminum silicate, magnesium silicate, calcium silicate, sodiumsilicate, potassium silicate, zirconium silicate, fused silica, mica,wollastonite, microlite, talc, MgO, Al₂O₃, TiO₂, ZrO₂, Y₂O₃, MgAl₂O₄,WO₂, E-glass fibers, TiB₂, ZrB₂, aluminum nitride, silicon nitride,silicon carbide, boron carbide, BaSO₄, CaF₂, AlF₃, MgAl, and TiAl. Inembodiments, the refractory charge comprises at least one of boronnitride, mica, zircon, talc, wollastonite, fused silica, siliconcarbide, microlite, barium sulfate, calcium fluoride, magnesiumfluorosilicate, graphite, bone ash, titanium dioxide, and aluminumfluoride. In embodiments, the refractory charge used to form the aqueousslurry of the present disclosure comprises at least one of wollastonite,fused silica, and silicon carbide.

In embodiments, the aqueous slurry formed in accordance with the methodof the present disclosure comprises 2 wt % to 10 wt % binder system, 40wt % to 75 wt % refractory charge, and 20 wt % to 50 wt % secondcolloidal binder. In embodiments, the aqueous slurry formed inaccordance with the method of the present disclosure comprises 2 wt % to10 wt % binder system, 40 wt % to 70 wt % refractory charge, and 25 wt %to 50 wt % second colloidal binder. In embodiments, the aqueous slurryformed in accordance with the method of the present disclosure comprises5 wt % to 10 wt % binder system, 45 wt % to 70 wt % refractory charge,and 25 wt % to 48 wt % second colloidal binder. Any of the previouslydescribed binder systems, refractory charges, and second colloidalbinders may be used to form the aqueous slurry of the presentdisclosure. In embodiments, the aqueous slurry formed in accordance withthe method of the present disclosure comprises: 2 wt % to 10 wt % bindersystem; 40 wt % to 75 wt % refractory charge comprising at least one ofwollastonite, fused silica, and silicon carbide; and 20 wt % to 50 wt %second colloidal binder comprising colloidal silica. In embodiments, theaqueous slurry formed in accordance with the method of the presentdisclosure comprises: 2 wt % to 10 wt % binder system; 60 wt % to 75 wt% refractory charge comprising at least one of wollastonite, fusedsilica, and silicon carbide; and 20 wt % to 50 wt % second colloidalbinder comprising colloidal silica. In embodiments, the aqueous slurryformed in accordance with the method of the present disclosurecomprises: 2 wt % to 10 wt % binder system; 65 wt % to 75 wt %refractory charge comprising at least one of wollastonite, fused silica,and silicon carbide; and 20 wt % to 50 wt % second colloidal bindercomprising colloidal silica.

In addition to the binder system, the refractory charge, and the secondcolloidal binder, the aqueous slurry of the present disclosure may alsoinclude one or more additives. Such additives may be present in theaqueous slurry in amount of less than 0.1 wt % based on the total weightof the aqueous slurry. Exemplary additives suitable for use in theaqueous slurry of the present disclosure include, but are not limitedto, rheology modifiers, dispersants, and plasticizers.

In accordance with the present disclosure, the method of making arefractory article includes casting the aqueous slurry into a mold. Themold may correspond to any desired shape for the refractory articlebeing produced. The mold may be formed of a variety of materialsincluding, but not limited to, cardboard, foams (e.g., polystyrene),metals, wood, plastics, natural polymers, and synthetic polymers.

In accordance with the present disclosure, the aqueous slurry is at aslurry casting temperature when the aqueous slurry is cast into themold. The slurry casting temperature may vary widely. In embodiments,the slurry casting temperature may be greater than 0° C. to less than100° C., including 1° C. to 80° C., 1° C. to 60° C., 5° C. to 50° C.,10° C. to 40° C., and also including 15° C. to 30° C.

The mold may be at various temperatures (e.g., room temperature (15° C.to 30°), above room temperature (>30° C.), below room temperature (<15°C.)) when the aqueous slurry is cast into the mold. In embodiments, themold may be at a temperature of 30° C. to 100° C. when the aqueousslurry is cast into the mold. In embodiments, the mold may be at atemperature of 15° C. to 30° C. when the aqueous slurry is cast into themold. In embodiments, the mold may be at a temperature of −195° C. to15° C. when the aqueous slurry is cast into the mold.

In embodiments, the method of the present disclosure further includesplacing one or more reinforcement material(s) into or on the mold.Examples of suitable reinforcement materials that may be incorporatedinto or on the mold include, but are not limited to, a high temperaturefabric (e.g., woven glass fiber mats, woven carbon fiber mats), glassfibers, refractory ceramic fibers, non-refractory ceramic fibers, carbonfibers, synthetic fibers (e.g., polymer fibers, polypropylene fibers),metal fibers (e.g., steel needles), mineral fibers, and metal anchoringof various sizes and geometries. In embodiments, the method of thepresent disclosure further includes adding one or more reinforcementmaterials (e.g., any one or more of the fiber materials described above,a refractory fiber material) directly into the aqueous slurry. Inembodiments, the method of the present disclosure includes placing alayer of a high temperature fabric, preferably a woven glass fiber mat,into or on the mold prior to casting the aqueous slurry into the mold.In embodiments, the method of the present disclosure includes placing alayer of a high temperature fabric, preferably a woven glass fiber mat,into or on the mold, casting a first portion of the aqueous slurry intothe mold, placing an additional layer of a high temperature fabric,preferably a woven glass fiber mat, on the first portion of the aqueousslurry cast into the mold, and casting a second portion of the aqueousslurry into the mold. This process may be repeated multiple times toform multiple layers of reinforcement material and aqueous slurry.However, it should be understood that the aqueous slurry may fullyimpregnate or saturate the multiple layers of reinforcement material(e.g., such that the reinforcement material is embedded in the aqueousslurry).

In accordance with the present disclosure, the method of making arefractory article includes subjecting the mold containing the aqueousslurry to a temperature and for a time sufficient to form a greenstrength article. In accordance with the present disclosure, the moldcontaining the aqueous slurry will be subjected to a temperature that islower than the slurry casting temperature. In other words, the aqueousslurry cast into the mold will solidify by subjecting the aqueous slurryto lower temperatures, thereby forming a green strength article. Forexample, the aqueous slurry cast into the mold will solidify byfreezing, thereby forming a green strength article. The step of forminga green strength article may be carried out using conventionaltechniques and equipment known to those of skill in the art (e.g.,freezers, exposure to liquid nitrogen). In embodiments, the moldcontaining the aqueous slurry is subjected to a temperature of −195° C.to 0° C. for a time sufficient to form the green strength article. Inembodiments, the mold containing the aqueous slurry is subjected to atemperature of −150° C. to 0° C., including a temperature of −125° C. to0° C., a temperature of −100° C. to −10° C., a temperature of −90° C. to−25° C., a temperature of −90° C. to −50° C., and also including atemperature of −85° C. to −75° C. for a time sufficient to form thegreen strength article. The time required to form the green strengtharticle may vary depending on a variety of parameters including, forexample, mass, shape/geometry, the aqueous slurry composition, and thetemperature at which the mold containing the aqueous slurry issubjected. In embodiments, the time required to form the green strengtharticle may be from 1 minute to 72 hours, including from 10 minutes to60 hours, 30 minutes to 48 hours, 1 hour to 36 hours, 2 hours to 24hours, from 6 hours to 24 hours, from 8 hours to 24 hours, from 12 hoursto 24 hours, from 18 hours to 24 hours, and also including from 24 hoursto 72 hours. In embodiments, the time required to form the greenstrength article may be from 1 minute to 1 hour.

The step of forming the green strength article from the aqueous slurryis critical to the method of the present disclosure. Without wishing tobe bound by any particular theory, it is believed that the binder systemutilized to form the aqueous slurry, particularly the caramelizedcarbohydrate component, and the step of forming the green strengtharticle by subjecting the mold containing the aqueous slurry to thetemperatures described herein synergistically produce the unique andadvantageous globular pore structure and isotropic distribution of poresin the refractory articles. Again, without wishing to be bound by anyparticular theory, a freeze-cast green strength article is believed tobe formed as the refractory charge particles in the aqueous slurry arerejected from the solidification front and trapped between the growingice crystals. This process is believed to be governed by the laws ofthermodynamics and the relationship in surface free energy between thesolidifying body, the liquid, and the individual refractory chargeparticles. It is believed that the caramelized carbohydrate component ofthe binder system alters both the viscosity of the liquid and thesurface free energy of the refractory charge particles, which changesthe extraction of the refractory charge particle from the ice front,resulting in the articles described herein. It is further believed thatthe caramelized carbohydrate component of the binder systems aids in thecontrolled removal of water from the system through evaporativesyneresis, which makes possible the ability to process the greenstrength article directly from a freezer (e.g., at −80° C.) to an oven(e.g., at 700° C.) with no intermediary steps (e.g., a drying step).Furthermore, and again, not wishing to be bound by any particulartheory, it is believed that underlying principle of the methods of thepresent disclosure and the resulting refractory articles are notstrongly dependent on the particular refractory charge used but relymore on physical interactions rather than chemical interactions.

Refractory articles that are freeze-casted without forming the greenstrength article in accordance with the present disclosure willgenerally have a lamellar porosity and a heterogeneous distribution ofpores as opposed to the globular pores and the isotropic distribution ofpores achieved with the methods of the present disclosure. As previouslymentioned, refractory articles having a lamellar porosity are oftenbrittle, prone to cracking, and typically exhibit strength in a uniaxialdirection.

In accordance with the present disclosure, the method of making arefractory article includes firing the green strength article at atemperature of at least 450° C. for a time sufficient to achieve thermalhomogeneity, thereby forming a refractory article. In embodiments, thegreen strength article is fired at an oven temperature of 450° C. to1,500° C., including an oven temperature of 550° C. to 1,250° C., anoven temperature of 550° C. to 1,200° C., an oven temperature of 600° C.to 1,150° C., an oven temperature of 650° C. to 1,100° C., an oventemperature of 675° C. to 1,000° C., an oven temperature of 675° C. to900° C., an oven temperature of 675° C. to 850° C., an oven temperatureof 675° C. to 800° C., and also including a temperature of 675° C. to725° C. for a time sufficient to achieve thermal homogeneity, therebyforming a refractory article. The time required to achieve thermalhomogeneity may vary depending on a variety of parameters including, forexample, the mass, the shape/geometry, the aqueous slurry compositionused to form the green strength article, and the temperature at whichthe green strength article is fired. In embodiments, the time requiredto achieve thermal homogeneity during firing will be from 0.5 hour to 24hours, including from 1 hour to 18 hours, from 1 hour to 12 hours, from1 hour to 8 hours, from 1 hour to 5 hours, and also including from 2hours to 3 hours. Firing of the green strength article may beaccomplished using conventional equipment such as an oven, furnace, orkiln.

In embodiments of the present disclosure, the method further includesdemolding the green strength article prior to firing the green strengtharticle. In embodiments of the present disclosure, the method includesfiring the mold and the green strength article and, thus, a demoldingstep is not required. In embodiments where the mold and green strengtharticle are fired together, the mold is formed of a material that willburn or otherwise decompose during firing, such as a cardboard or a foammaterial.

In embodiments of the present disclosure, the method does not includedrying the green strength article prior to firing. In other words, thegreen strength article (containing solidified water) may be firedimmediately without additional processing. Conventional processestypically utilize a drying step to remove water or other solvents priorto firing. However, the method of the present disclosure does notrequire such a drying step to form a refractory article having theunique pore structure and advantages described herein. Furthermore,eliminating the conventional drying step provides economic advantages,as a drying step requires floor space, equipment, man power, andplanning. While a drying step is not required and, indeed is notpreferred, in other embodiments, the method of the present disclosuremay include drying the green strength article prior to firing. Thedrying step may be accomplished using drying equipment (e.g., an oven, afreeze dryer) or by letting the green strength article dry naturally atambient or room temperature.

In embodiments, the method of the present disclosure includes coolingthe refractory article after the firing step. In embodiments, thecooling step may be performed by allowing the refractory article to coolnaturally at ambient or room temperature. In embodiments, the coolingstep may be performed in controlled stages. For example, the refractoryarticle, after firing, may be cooled by allowing the oven to cool to apredetermined temperature, opening the oven for a predetermined time,and removing the refractory article from the oven. The particularparameters of the controlled stages of the cooling step will typicallydepend on the size and the shape of the refractory article, as well asthe particular refractory charge. One of skill in the art can readilydetermine the particular parameters of the controlled stages of thecooling step with routine experimentation.

The methods of the present disclosure produce refractory articles havinga number of unique features and advantages including, but not limitedto, an open and globular porosity, an isotropic pore distribution, a lowdensity, a higher strength to density ratio, and net shape. The opennessof the porosity allows fluids to easily flow through the refractoryarticle matrix, which may be advantageous in filtration applications orwhen dispersing a beneficial liquid such as a lubricant, catalyst, orprotective coating throughout the refractory article. The globular shapeof the pores may provide better resistance to crack initiation and/orcrack propagation in the refractory article. By having a low density,the refractory articles formed in accordance with the methods of thepresent disclosure may be lighter, which can reduce stresses oncomponents that mate with or otherwise join to a refractory article, aswell as improve safety for process operators (e.g., the lighter articleis easier to lift). Furthermore, the low density can improve thebuoyancy of the refractory article in a molten metal (e.g., if arefractory article breaks, the pieces will float on top of the moltenmetal and can be easily removed). The strength of the refractory articleprovides resistance to mechanical solicitation (e.g., pressure,abrasion, deformation, creep, etc.) to enhance the life span of therefractory article. The isotropic distribution of pores is believed toprovide the refractory articles made in accordance with the methods ofthe present disclosure with a greater homogeneity of strength, as wellas an improved strength to weight ratio (or strength to density ratio).In addition, refractory articles formed in accordance with the methodsof the present disclosure are net shape with very low or no shrinkage ordeformation relative to the mold shape. Minimizing the amount ofshrinkage opens the door for more complex shapes, tighter tolerances,less finishing process time required, and reduced potential forin-process scrap from thermal stresses. Although the refractory articlesgenerally have a net shape or a near net shape, the refractory articlesformed in accordance with the methods of the present disclosure may alsobe machined to a desired shape and/or finish.

A variety of refractory articles for a variety of applications may beproduced using the methods of the present disclosure. Refractoryarticles that may be made in accordance with the methods of the presentdisclosure include, but are not limited to, monolithic big blocks (forfurnace walls), ladles, spouts, launders, dosing tubes, plungers, pins,floats, tundish, head box, crucibles, burner tips, filters,insulating/conducting bricks, insulating/conducting boards, diffusers,and absorbents.

In embodiments, the refractory article made in accordance with themethods of the present disclosure has an apparent porosity, as measuredin accordance with ASTM C830, of 35% to 65%. In embodiments, therefractory article made in accordance with the methods of the presentdisclosure has an apparent porosity of 35% to 60%, including an apparentporosity of 40% to 60%, and also including an apparent porosity of 45%to 55%.

In embodiments, the refractory article made in accordance with themethods of the present disclosure has a bulk density, as measured inaccordance with ASTM C830, of 1 g/cm³ to 2.5 g/cm³, including a bulkdensity of 1 g/cm³ to 2.2 g/cm³, a bulk density of 1.05 g/cm³ to 2.15g/cm³, a bulk density of 1.1 g/cm³ to 2.1 g/cm³, a bulk density of 1.15g/cm³ to 2.05 g/cm³, a bulk density of 1.25 g/cm³ to 1.9 g/cm³, a bulkdensity of 1.3 g/cm³ to 1.6 g/cm³, and also including a bulk density of1.1 g/cm³ to 1.65 g/cm³.

In embodiments, the refractory article made in accordance with themethods of the present disclosure has a specific density, as measured inaccordance with ASTM C830, of 2.15 g/cm³ to 3.75 g/cm³, including aspecific density of 2.2 g/cm³ to 3.7 g/cm³, a specific density of 2.5g/cm³ to 3.1 g/cm³, a specific density of 2.6 g/cm³ to 3 g/cm³, and alsoincluding a specific density of 2.7 g/cm³ to 2.9 g/cm³.

In embodiments, the refractory article made in accordance with themethods of the present disclosure has a cold crush strength (CCS), asmeasured in accordance with a modified version of ASTM C133 (by using a1.5 inch×1.5 inch×2 inch specimen as opposed to the standard 2 inch×2inch×2 inch specimen), of 4 MPa to 25 MPa, including a CCS of 4.5 MPa to22 MPa, a CCS of 4.65 MPa to 20 MPa, a CCS of 5 MPa to 15 MPa, a CCS of5.5 MPa to 10 MPa, a cold crush strength of 10 MPa to 25 MPa, a CCS of15 MPa to 25 MPa, and also including a CCS of 17 MPa to 22 MPa. The CCSrepresents the ability of the refractory article to resist failure undercompressive load at room temperature. The CCS can also be viewed asrepresenting the bonding strength of the constituents of the refractoryarticle when tested in compression.

In embodiments, the refractory article made in accordance with themethods of the present disclosure has a dimensional shrinkage (as anabsolute value) of 0% to 0.3%, including a dimensional shrinkage of0.01% to 0.25%, and also including a dimensional shrinkage of 0.01% to0.15%. Dimensional shrinkage may be determined by measuring a dimensionof the green strength article and a dimension of the refractory article,determining the difference between the dimension of the green strengtharticle and the dimension of the refractory article, and dividing thedifference by the dimension of the green strength article. Such adimensional shrinkage indicates that the methods of the presentdisclosure can be used to form refractory articles having a net shape.

In embodiments, the refractory article made in accordance with themethods of the present disclosure has a cold modulus of rupture (CMOR),as measured in accordance with a modified version of ASTM C133 (by usingan 8 inch×1.5 inch×2 inch specimen as opposed to the standard 9 inch×2inch×2 inch specimen), of 1 MPa to 3.5 MPa, including a CMOR of 1.05 MPato 3.3 MPa, a CMOR of 1.1 MPa to 3.25 MPa, a CMOR of 1.25 MPa to 3 MPa,a CMOR of 1.5 MPa to 2.5 MPa, a CMOR of 1.75 MPa to 2.25 MPa, a CMOR of1 MPa to 2 MPa, a CMOR of 1.75 MPa to 3.3 MPa, and also including a CMORof 2 MPa to 3.25 MPa. The CMOR is an important parameter of therefractory article, as it represents the strength of the refractoryarticle at the limit of its elastic domain. The CMOR is determined usinga destructive test.

In embodiments, the refractory article made in accordance with themethods of the present disclosure has a bulk density of 1 g/cm³ to 2.2g/cm³, an apparent porosity of 35% to 65%, and a ratio of CCS to bulkdensity of 3 MPa/g/cm³ to 15 MPa/g/cm³. In certain embodiments, therefractory article made in accordance with the methods of the presentdisclosure has a bulk density of 1 g/cm³ to 2.2 g/cm³, an apparentporosity of 35% to 65%, and a ratio of CCS to bulk density of 3.5MPa/g/cm³ to 14.5 MPa/g/cm³, including a ratio of CCS to bulk density of4 MPa/g/cm³ to 14 MPa/g/cm³, a ratio of CCS to bulk density of 4.1MPa/g/cm³ to 13.75 MPa/g/cm³, and also including a ratio of CC S to bulkdensity of 5 MPa/g/cm³ to 13.75 MPa/g/cm³. In embodiments, therefractory article made in accordance with the methods of the presentdisclosure has a bulk density of 1.1 g/cm³ to 2.1 g/cm³, an apparentporosity of 35% to 60%, and a ratio of CCS to bulk density of 4MPa/g/cm³ to 15 MPa/g/cm³. In embodiments, the refractory article madein accordance with the methods of the present disclosure has a bulkdensity of 1.12 g/cm³ to 2 g/cm³, an apparent porosity of 40% to 60%,and a ratio of CCS to bulk density of 4 MPa/g/cm³ to 14 MPa/g/cm³. Inembodiments, the refractory article made in accordance with the methodsof the present disclosure has a bulk density of 1.1 g/cm³ to 1.7 g/cm³,an apparent porosity of 40% to 60%, and a ratio of CCS to bulk densityof 4 MPa/g/cm³ to 15 MPa/g/cm³, including a ratio of CCS to bulk densityof 4.1 MPa/g/cm³ to 14 MPa/g/cm³, and also including a ratio of CCS tobulk density of 10 MPa/g/cm³ to 15 MPa/g/cm³. The ratio of CCS to bulkdensity is a normalization referred to as “specific cold crushstrength.” Such a normalization is useful to compare the CCS ofdifferent materials.

In embodiments, the refractory article made according to the methods ofthe present disclosure has a bulk density of 1 g/cm³ to 2.5 g/cm³ and aratio of CMOR to bulk density of 0.5 MPa/g/cm³ to 15 MPa/g/cm³. Inembodiments, the refractory article made according to the methods of thepresent disclosure has a bulk density of 1 g/cm³ to 2.5 g/cm³ and aratio of CMOR to bulk density of 0.5 MPa/g/cm³ to 10 MPa/g/cm³. Inembodiments, the refractory article made according to the methods of thepresent disclosure has a bulk density of 1 g/cm³ to 2.5 g/cm³ and aratio of CMOR to bulk density of 0.5 MPa/g/cm³ to 8 MPa/g/cm³. Inembodiments, the refractory article made according to the methods of thepresent disclosure has a bulk density of 1 g/cm³ to 2.5 g/cm³ and aratio of CMOR to bulk density of 0.5 MPa/g/cm³ to 6 MPa/g/cm³. Inembodiments, the refractory article made according to the methods of thepresent disclosure has a bulk density of 1 g/cm³ to 2.2 g/cm³, anapparent porosity of 35% to 65%, and a ratio of CMOR to bulk density of0.65 MPa/g/cm³ to 3 MPa/g/cm³. In embodiments, the refractory articlemade according to the methods of the present disclosure has a bulkdensity of 1 g/cm³ to 2.2 g/cm³, an apparent porosity of 35% to 65%, anda ratio of CMOR to bulk density of 0.65 MPa/g/cm³ to 2.5 MPa/g/cm³,including a ratio of CMOR to bulk density of 0.75 MPa/g/cm³ to 2.25MPa/g/cm³, a ratio of CMOR to bulk density of 0.85 MPa/g/cm³ to 2.1MPa/g/cm³, and also including a ratio of CMOR to bulk density of 0.95MPa/g/cm³ to 2.05 MPa/g/cm³. In embodiments, the refractory article madeaccording to the methods of the present disclosure has a bulk density of1.1 g/cm³ to 2.1 g/cm³, an apparent porosity of 35% to 60%, and a ratioof CMOR to bulk density of 0.75 MPa/g/cm³ to 2.1 MPa/g/cm³. Inembodiments, the refractory article made according to the methods of thepresent disclosure has a bulk density of 1.12 g/cm³ to 2 g/cm³, anapparent porosity of 40% to 60%, and a ratio of CMOR to bulk density of0.85 MPa/g/cm³ to 2.1 MPa/g/cm³. The ratio of CMOR to bulk density is anormalization referred to as “specific cold modulus of rupture.” Such anormalization is useful to compare the CMOR of different materials.

In embodiments, the refractory article made according to the methods ofthe present disclosure has a bulk density of 1 g/cm³ to 2.2 g/cm³, anapparent porosity of 35% to 65%, and an isotropic distribution of pores.In embodiments, the refractory article made according to the methods ofthe present disclosure has a bulk density of 1 g/cm³ to 2.2 g/cm³, anapparent porosity of 35% to 65%, a CCS, as measured in accordance with amodified version of ASTM C133 (by using a 1.5 inch×1.5 inch×2 inchspecimen as opposed to the standard 2 inch×2 inch×2 inch specimen), of 4MPa to 25 MPa, and an isotropic distribution of pores. In embodiments,the refractory article made according to the methods of the presentdisclosure has a bulk density of 1 g/cm³ to 2.2 g/cm³, an apparentporosity of 35% to 65%, a CMOR, as measured in accordance with amodified version of ASTM C133 (by using an 8 inch×1.5 inch×2 inchspecimen as opposed to the standard 9 inch×2 inch×2 inch specimen), of 1MPa to 3.5 MPa, and an isotropic distribution of pores. In embodiments,the refractory article made in accordance with the methods of thepresent disclosure has a bulk density of 1 g/cm³ to 2.2 g/cm³, anapparent porosity of 35% to 65%, a ratio of CCS to bulk density of 3MPa/g/cm³ to 15 MPa/g/cm³, and an isotropic distribution of pores.

As mentioned above, the methods of the present disclosure may include astep in which a refractory fiber material is added to the aqueous slurryprior to casting the aqueous slurry in the mold, to provide a fiberreinforced refractory article. In such embodiments, the fiber reinforcedrefractory article made according to the methods of the presentdisclosure may have a bulk density of 1 g/cm³ to 2.5 g/cm³ and a ratioof cold modulus of rupture (CMOR) to bulk density of 6 MPa/g/cm³ to 15MPa/g/cm³. In embodiments, the fiber reinforced refractory article madeaccording to the methods of the present disclosure may have a bulkdensity of 1.1 g/cm³ to 2.5 g/cm³ and a ratio of CMOR to bulk density of8 MPa/g/cm³ to 15 MPa/g/cm³. In embodiments, the fiber reinforcedrefractory article made according to the methods of the presentdisclosure may have a bulk density of 1.2 g/cm³ to 2.5 g/cm³ and a ratioof CMOR to bulk density of 10 MPa/g/cm³ to 15 MPa/g/cm³. In embodiments,the fiber reinforced refractory article made according to the methods ofthe present disclosure may have a bulk density of 1.5 g/cm³ to 2.5 g/cm³and a ratio of CMOR to bulk density of 12 MPa/g/cm³ to 15 MPa/g/cm³. Inembodiments, the fiber reinforced refractory article made according tothe methods of the present disclosure may have a bulk density of 1 g/cm³to 2.5 g/cm³ and a ratio of CMOR to bulk density of 6 MPa/g/cm³ to 10MPa/g/cm³. When reinforced with refractory fiber material, therefractory articles will typically be less porous because the volumeoccupied by the refractory fiber material will not participate in thepore formation process, but will exhibit a higher strength, asdemonstrated by a higher ratio of CMOR to bulk density.

EXAMPLE

The example that follows illustrates certain exemplary embodiments ofrefractory articles made in accordance with the methods of the presentdisclosure. The example is given solely for the purpose of illustrationand is not to be construed as limiting of the present disclosure, asmany variations thereof are possible without departing from the spiritand scope of the present disclosure.

Three samples (Samples A-C) of refractory articles were made inaccordance with the methods of the present disclosure. To make eachsample, an aqueous slurry was formed. The aqueous slurry used to makeeach sample included a mixture of a binder system, a refractory charge,and a second colloidal binder. The weight percentage (based on the totalweight of the aqueous slurry) of each component used to form eachaqueous slurry (Slurries A-C) is listed below in Table 1.

In addition, three comparative samples (Samples 1-3) of refractoryarticles were prepared. To make each comparative sample, a comparativeaqueous slurry was formed. The comparative aqueous slurry was similar tothe aqueous slurry used to form Samples A-C, but did not include thebinder system of the present disclosure. The weight percentage (based onthe total weight of the comparative aqueous slurry) of each componentused to form each comparative aqueous slurry (Slurries 1-3) is listedbelow in Table 1.

TABLE 1 Aqueous Slurry Compositions Slurry A Slurry 1 Slurry B Slurry 2Slurry C Slurry 3 Components (wt %) (wt %) (wt %) (wt %) (wt %) (wt %)Wollastonite 46 50 — — — — (refractory charge) Fused Silica — — 63 67 —— (refractory charge) Silicon Carbide — — — — 63 67 (refractory charge)Colloidal Silica 46 50 31 33 31 33 (second colloidal binder) BinderSystem  8 —  6 —  6 —

The binder system was the same composition for each of Slurries A-C andwas prepared as follows. A one kilogram mixture was prepared by mixingtogether the following ingredients in a stainless steel container: a)food grade table sugar (i.e., sucrose) from Lantic, Inc. (Montreal,Quebec, Canada); b) water; c) laboratory grade phosphoric acid 75 wt %(i.e., a mixture of 75 wt % H₃PO₄ and 25 wt % water); d) calciumphosphate monobasic, including Ca(H₂PO₄)·H₂O, from Spectrum ChemicalManufacturing Corp. (New Brunswick, N.J.); and e) laboratory gradealuminum ammonium sulfate, including AlNH₄(SO₄)₂·12 H₂O, from ACPChemicals, Inc. (Saint-Léonard, Quebec, Canada).

The mixture was prepared by adding 550 grams of sucrose, 415 grams ofwater, 11 grams of phosphoric acid (75 wt %), 14 grams of calciumphosphate monobasic, and 10 grams of aluminum ammonium sulfate into astainless steel container, and then mixing the ingredients together witha paint mixer until a homogenous mixture was obtained.

The homogenous mixture was then heated to a temperature of 80° C. to120° C. and held at this temperature for at least 5 minutes to form acaramelized carbohydrate component. The caramelized carbohydratecomponent was allowed to cool at room temperature (e.g., 20° C. to 25°C.).

Next, 515 grams of a first colloidal binder was added to the 1 kilogramof caramelized carbohydrate component. The first colloidal binder wasNALCO 1144 colloidal silica available from Nalco Company (Naperville,Ill.). The colloidal silica and the caramelized carbohydrate componentwere then mixed together using the paint mixer to form the bindersystem. The mixing was carried out at room temperature (e.g., 20° C. to25° C.) for a time sufficient to obtain a homogenous binder system (inthis case, about 10 minutes).

The requisite amounts of the binder system, the refractory charge, andthe second colloidal binder (as indicated in Table 1) were mixedtogether to form Slurries A-C. A small amount (i.e., about 0.05 wt %) ofa rheology modifier (Nalco 625, commercially available from Nalco(Naperville, Ill.)) was added to each of Slurries A-C just prior tocasting each aqueous slurry. Next, each aqueous slurry was cast into amold, and the molds containing the slurries were placed in a freezer ata freezer temperature of −80° C. and held in the freezer overnight(e.g., for about 18-24 hours). The slurries solidified in the mold toform green strength articles, which were demolded and immediately firedin an oven at an oven temperature of 700° C. for 2-3 hours to producethe refractory article samples (i.e., Samples A-C, which correspond toSlurries A-C). The resulting refractory article samples were tested forvarious physical and mechanical properties, as shown below in Table 2.The comparative samples (Samples 1-3) were prepared in a similar fashionas described above for Samples A-C, and were tested for the samephysical and mechanical properties, the results of which are also shownin Table 2.

TABLE 2 Properties of Refractory Article Samples Analytical SampleSample Sample Sample Sample Sample Property Method A 1 B 2 C 3 Bulkdensity ASTM 1.14* 1.23 1.30* 1.41 1.60* 1.76 (g/cm³) C830 Specificdensity ASTM 2.70  2.70 2.21  2.22 2.99  2.99 (g/cm³) C830 Apparent ASTM58*    55 41*    36 47*    41 porosity (%) C830 Dimensional — −0.24 0.21 −0.15*  −0.02 0.03  0.04 shrinkage (%) Cold Crush ASTM 4.68* 3.1017.06*  6.10 21.80*  9.13 Strength (CCS) C133 (MPa) Cold Modulus of ASTM1.11* 0.50 1.84* 0.66 3.20* 1.32 Rupture C133 (CMOR) (MPa) Ratio of CCSto — 4.12* 2.53 13.08*  4.33 13.64*  5.19 Bulk Density Ratio of CMOR —0.98* 0.41 1.49* 0.43 2.00* 0.75 to Bulk Density *Indicatesstatistically significant difference for the presence of the bindersystem (ANOVA, p = 0.05).

As seen in Table 2, the refractory articles formed in accordance withthe present disclosure (Samples A-C) exhibited statistically significanthigher cold crush strength and cold modulus of rupture values ascompared to the comparative refractory articles (Samples 1-3). Inaddition, the apparent porosity values for Samples A-C werestatistically significantly higher than the apparent porosity values forcomparative Sample 1-3. Furthermore, the ratio of cold crush strength tobulk density and the ratio of cold modulus of rupture to bulk densitywere also statistically significantly higher for Samples A-C as comparedto comparative Samples 1-3. These ratios indicate that the refractoryarticles made in accordance with the present disclosure (Samples A-C)are mechanically stronger than the comparative refractory articles(Samples 1-3).

It is believed that the improved strength exhibited by Samples A-Cresults from the isotropic distribution of pores created using themethods of the present disclosure. FIG. 1 shows an optical digitalmicroscope image of the refractory article corresponding to Sample C,which uses silicon carbide as the refractory charge. As seen in FIG. 1,the pores of the refractory article have a uniform size, shape, anddistribution throughout the refractory article. On the other hand, FIG.2 shows a similar image of the comparative refractory articlecorresponding to Sample 3, which also uses silicon carbide as therefractory charge. Unlike the isotropic distribution of pores of SampleC shown in FIG. 1, the pores of Sample 3 as shown in FIG. 2 clearly donot have a uniform size, shape, or distribution throughout therefractory article of Sample 3.

While the present disclosure has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the present disclosure, in itsbroader aspects, is not limited to the specific details, therepresentative compositions and processes, and illustrative examplesshown and described. Accordingly, departures may be made from suchdetails without departing from the spirit or scope of the presentdisclosure.

What is claimed is:
 1. A method of making a refractory article, themethod comprising: a) mixing a binder system, a refractory charge, and asecond colloidal binder to form an aqueous slurry; b) casting theaqueous slurry into a mold, wherein the aqueous slurry is at a slurrycasting temperature; c) subjecting the mold containing the aqueousslurry to a temperature that is less than the slurry casting temperaturefor a time sufficient to form a green strength article; and d) firingthe green strength article at a temperature of at least 450° C. for atime sufficient to achieve thermal homogeneity, thereby forming arefractory article.
 2. The method of claim 1, further comprising placinga reinforcement material into or on the mold.
 3. The method of claim 1,wherein the mold containing the aqueous slurry is subjected to atemperature of −195° C. to 0° C.
 4. The method of claim 1, wherein themold containing the aqueous slurry is subjected to a temperature of−100° C. to -30° C.
 5. The method of claim 1, further comprisingdemolding the green strength article.
 6. The method of claim 1, whereinthe green strength article is not subjected to a drying step prior tothe firing step.
 7. The method of claim 1, further comprising formingthe binder system, wherein forming the binder system comprises:preparing a mixture comprising water and a carbohydrate; heating themixture to a caramelization temperature for an effective amount of timeto caramelize the carbohydrate and form a caramelized carbohydratecomponent; and mixing the caramelized carbohydrate component with afirst colloidal binder and an adjuvant to form the binder system.
 8. Themethod of claim 1, wherein the binder system comprises a caramelizedcarbohydrate component, a first colloidal binder, and an adjuvant. 9.The method of claim 8, wherein the caramelized carbohydrate component isderived from at least one of sucrose, glucose, fructose, galactose,maltose, or lactose.
 10. The method of claim 8, wherein the firstcolloidal binder comprises at least one of a colloidal silica, acolloidal alumina, a colloidal zirconia, a colloidal yttria, anorganically modified colloidal silica, an organically modified colloidalalumina, an organically modified colloidal zirconia, or an organicallymodified colloidal yttria.
 11. The method of claim 8, wherein theadjuvant comprises at least one of an acid, an inorganic wetting agent,or an acid phosphate adhesive.
 12. The method of claim 11, wherein whenthe adjuvant comprises an acid, the acid comprises at least one ofphosphoric acid, sulfuric acid, citric acid, acetic acid, boric acid, oroxalic acid; wherein when the adjuvant comprises an inorganic wettingagent, the inorganic wetting agent comprises at least one of aluminumammonium sulfate, magnesium sulfate, aluminum sulfate, or calciumsulfate; and wherein when the adjuvant comprises an acid phosphateadhesive, the acid phosphate adhesive comprises at least one of calciumphosphate, magnesium phosphate, or aluminum phosphate.
 13. The method ofclaim 8, wherein the caramelized carbohydrate component comprises from 5wt % to 70 wt % of the binder system, the adjuvant comprises from 0.25wt % to 10 wt % of the binder system, and the first colloidal bindercomprises from 25 wt % to 90 wt % of the binder system.
 14. The methodof claim 1, wherein the refractory charge comprises at least one of asilicate, a metal oxide, a boride, a nitride, a carbide, a sulfide, afluoride, an aluminide, a synthetic glass, glass fibers, refractoryceramic fibers, non-refractory ceramic fibers, graphite, bone ash,aluminum titanate, or calcium aluminate.
 15. The method of claim 1,wherein the second colloidal binder comprises at least one of acolloidal silica, a colloidal alumina, a colloidal zirconia, a colloidalyttria, an organically modified colloidal silica, an organicallymodified colloidal alumina, an organically modified colloidal zirconia,or an organically modified colloidal yttria.
 16. The method of claim 1,further comprising cooling the refractory article after the firing step.17. The method of claim 1, wherein the binder system comprises from 2 wt% to 10 wt % of the aqueous slurry, the refractory charge comprises from40 wt % to 75 wt % of the aqueous slurry, and the second colloidalbinder comprises from 20 wt % to 50 wt % of the aqueous slurry.
 18. Arefractory article made according to the method of claim
 1. 19. Arefractory article made according to the method of claim 1, wherein therefractory article is characterized by a bulk density of 1 g/cm³ to 2.2g/cm³, an apparent porosity of 35% to 65%, and a ratio of cold crushstrength to bulk density of 4 MPa/g/cm³ to 25 MPa/g/cm³.
 20. Arefractory article made according to the method of claim 1, wherein therefractory article is characterized by a bulk density of 1 g/cm³ to 2.2g/cm³, an apparent porosity of 35% to 65%, and a ratio of cold modulusof rupture to bulk density of 0.6 MPa/g/cm³ to 2.5 MPa/g/cm³.
 21. Arefractory article made according to the method of claim 1, wherein therefractory article is characterized by a bulk density of 1 g/cm³ to 2.2g/cm³, an apparent porosity of 35% to 65%, and an isotropic distributionof pores.
 22. A refractory article made according to the method of claim1, wherein the refractory article is reinforced with a refractory fibermaterial, wherein the refractory article has a bulk density of 1 g/cm³to 2.5 g/cm³ and a ratio of cold modulus of rupture to bulk density of 6MPa/g/cm³ to 15 MPa/g/cm³.